This invention relates to a mechanism for application to internal combustion engines.
The mechanism concerns a piston and drive shaft coupling. The coupling communicates energy from the piston to an engine""s drive shaft in a manner that permits the piston to move in a predetermined characteristic different from the generally sinusoidal characteristic resulting from a conventional piston coupling.
This mechanism may be applied to either a two-stroke or four-stroke internal combustion engine.
It is known in multi-cylinder internal combustion piston engines to provide a single crankshaft to which each piston is attached by means of a connecting rod. When the crankshaft is rotating at constant speed, each upstroke and downstroke of the piston has the same duration. The movement of each piston is characterised approximately by a sine wave which indicates the position of the piston in the cylinder as a function of the rotational position of the drive shaft.
It is desirable for a number of reasons including optimising combustion efficiency, increasing fuel economy, maximising power output, increasing torque, reducing mechanical stresses, or generally enhancing tuning flexibility to be able to modify the characteristic relationship between the motion of the piston and the drive shaft. Hitherto, attempts to do this have been largely unsuccessful.
It is an object of the present invention to overcome or substantially ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative.
According to a first aspect of the invention, there is provided an internal combustion engine including:
a drive shaft;
a crank including a crank pin;
a piston mounted for reciprocation within a cylinder;
a connecting rod extending between the piston and the crank pin;
a first crank gear mounted on the crank; and
a first drive gear mounted on the drive shaft;
wherein the first crank gear and the first drive gear form a first gear pair;
wherein said first gear pair is drivingly engaged for at least a first portion of a complete revolution of the drive shaft; and
wherein at least one of the first crank gear and the first drive gear of said first gear pair is non-elliptical;
such that reciprocation of the piston causes rotation of the drive shaft in a relationship determined by the respective profiles of the crank gear and the drive gear of the first gear pair.
Preferably, the first drive gear and the first crank gear have an equal number of teeth so that one revolution of the crank gear produces one revolution of the drive shaft. Preferably also, the crank gear and the drive gear are both non-elliptical.
In one preferred embodiment, one or other of the drive gear and the crank gear is eccentrically mounted to the drive shaft or the crank respectively. Alternatively, both the drive gear and the crank gear may be eccentrically mounted. In a preferred form, the crank gear is integral with the crank.
In another preferred form, the engine further includes:
a second crank gear mounted to the crank; and
a second complementary drive gear mounted to the drive shaft;
wherein said second crank gear and second drive gear form a second gear pair;
wherein the second gear pair is drivingly engaged for at least a second complementary portion of a complete revolution of the drive shaft; and
wherein at least one of the second crank gear and the second drive gear of said second gear pair is non-circular;
such that reciprocation of the piston causes rotation of the drive shaft in a relationship determined by the profiles of the crank gears and the drive gears of the respective first and second gear pairs.
More preferably, the first and second crank gears are different in circumferential length. The first and second drive gears are preferably formed as a single composite gear having a first portion engaged with the first crank gear for the duration of one complete revolution of the crank, and a second portion engaged with the second crank gear for the duration of a subsequent complete revolution of the crank, thereby providing one drive shaft revolution per two crank gear revolutions.
Still more preferably, the crank gear and the drive gear of each gear pair are both non-circular. In other preferred forms, one or both of the gears of each gear pair are eccentrically mounted respectively to their drive shaft or crank.
In a further preferred form, the engine includes a plurality of pistons and a single drive shaft, wherein each piston has an associated crank including a crank pin, a connecting rod extending between the piston and the crank pin, a first crank gear mounted to the crank and a first drive gear mounted to the drive shaft.
Still more preferably, all of the respective cranks are joined by a single crankshaft having a plurality of crank pins.